The current approach utilized in our immune reconstitution trials for pediatric sarcomas involves the adoptive transfer of T cells derived from patients prior to the administration of cytotoxic chemotherapy. This approach is used because peripheral expansion of mature T cells represents the primary pathway for T cell regeneration in the immediate post-chemotherapy period and even limited cycles of chemotherapy induce significant T cell depletion. Unfortunately, these products are contaminated with tumor cells in approximately 50-80% of cases. Similarly, a high incidence of tumor cell contamination has been observed in peripheral blood stem cell products used extensively in the context of autologous BMT for these tumors. Because such contaminating tumor cells have been shown to contribute to tumor recurrence in other pediatric tumors, a primary goal is the elimination of contaminating tumor cells in the cellular products used in the context of these therapies. To this end, we are currently studying a monoclonal antibody in collaboration with Dr. Nai-Kong Cheung of Memorial Sloan Kettering Cancer Center. This moab (8H9) shows excellent binding to osteosarcoma, Ewings sarcoma, neuroblastoma and rhabdomyosarcoma cell lines in our laboratory by flow cytometric analysis. In addition, we show no evidence of binding to stem cell populations (CD34+), T cells or other hematologic populations. Therefore, current work is focused on the utilization of magnetic bead selection to purge these cell populations of contaminating tumor cells. In order to document removal of tumor cells, we are utilizing quantitative polymerase chain reaction which amplifies the fusion proteins present in Ewings sarcoma and alveolar rhabdomyosarcoma. Currently, this technique is able to detect the equivalent of one Ewing?s sarcoma cell in 10,000 peripheral blood mononuclear cells and our most recent results with nested techniques appear to improve the level of sensitivity even further. - Ewing's sarcoma family of tumors (ESFT), cancer antigens, rhabdomyosarcoma, Bone marrow transplantation, immunotherapy, - Human Tissues, Fluids, Cells, etc.